Oscillograph apparatus



Sept. 21, 1948. BIAS ETAL 2,449,801

OSCILLOGRAPH APPARATUS Filed Nov. 1'7, 1944 V) 5; U U g v I I B Q m I I5 5 g Inventors: VI Frank J. Bias, m Harold W Lord,

uhl w Lgfizg y W Them Attorney.

Patented Sept. 21, 1948 Frank J Bias, Scotia, and Harold W.- Lord,Schenectady, N. Y.,-assignors to General 'Electric Company,

a, corporation of New York Application November 17, 1944, Serial Nscsszo' 7.2 Claims. (Cl. 315-24) Our invention relates to apparatus foranalyzing electric oscillations, and particularlyto cathode rayoscillographs of the type used forywave analysis or in connection withradio detectionand direction finding equipment.

It is a general object of our invention to provide a new and improvedcathode ray oscillograph apparatus including means-for synchronizing theoperation of a source of oscillations to be observed or analyzed Withthetiming sweep of the electron beam. I

It is a still further object of our invention to provide a cathode rayoscillograph apparatus in which a single source of recurrent voltagepulses synchronously controls the sweep of an electron beam, theintensity of the beam, and the"trigger circuit controlling the source ofoscillations to be analyzed. Our invention itself, togetherwith'furtherobjects and advantages thereof, will be more fullyunderstood by referring now to the following detailed specificationtaken in conjunction with the accompanying drawing, the single figureofwhich is a schematic circuit diagram of a cathoderay oscillographapparatus embodying our invention; Referring now to the drawing, Wehave-shown our invention applied to a cathode-ray-osciilograph apparatuscomprising a cathode-raydisl-e charge device I, a source 2 ofelectricoscillations to be observed, and a source 3 of substantiallyconstant frequency oscillations controlling the sweep and intensity ofthe electron beam and synchronizing the operation of the source with thebeam sweep. i

The source of sine wave voltage 3 may bean oscillator of any well-knowntype, such as a crystal or resonant circuit oscillator, and preferablyincludes suitable means, such as a variable candenser, inductance, orthe like controlledby a dial 4 for varying the frequency of thegenerated oscillations. The sine wave oscillations of selectableconstant frequency from the source 3 are amplified and distorted by anamplifier 5 and supplied to a differentiating circuit comprising a:apacitor E and a resistor 7 connected across the )utput of theamplifier 5. I

A transformer 8 having its primary winding 9 :onnected across theresistor 7 supplies from its econdary winding ill a series ofrecurrentvoltage pulses to the input of an amplifying electron lischargedevice If having an anode Ila conlected to a source of positiveunidirectional poential B|-. The input circuit of the'discharge ,evice Iincludes asource of negative bias potenial suchas a battery 112connected in'series c'i'r-' cuit relation'with the transformer windingl0 and agrid bias resistor IS. The high frequency oscillations from thetransformer winding [0 are supplied to thecontrol electrode of thedischarge device ll through acapacitor [4 connected in parallel circuitrelation'with the resistor l3; It will be understood that; because ofdifierentiaticn of the distorted amplifier outputwave in the circuit 6,1, the output-of the transformer 8 comprises an alternate series ofpositive and negative pulses. The negative voltage pulses supplied tothecontrol electrode of the discharge device-H have no effect, since thecontrol electrode-is normallybiased-negative and any negative voltagepulse serves only-to drive the discharge device ,ll farther into thecut-off region. The positive pulses from the transformerwinding l 0,however, overcome the negative bias from the source l2 thereby to renderthe discharge device 'Il recurrently conductive 'forshort intervals at afrequency determined by the frequency of the source 3, f

The positive voltage pulses supplied to the input of the -dischargedevice H are amplified andsupplied'as negative pulses from the anode ofthe device II to the anode of a regenerative pulse generating electrondischarge device I5 having an'anode l6, a cathode I l and a controlelectrode l8. In response tothe triggeringimpulses supplied to-the discharge' device [5 from the. discharge device If a pulsegenerating circuitassociated with the device 15 produces a' series of'recurrent voltagepulses having a frequency equal to the frequency of thetriggeringpulses. The pulse generating circuit associated with the dischargedeviceI5 includes'a'pulse transformer l9 and a pulse -formin'g andpulse-determining ca- Dacitive storage element 20. The capacitiveelement 20 is preferably constitutedby an openended artificialtransmission line section made up of'capacitors 2| and inductahces-ZZ.The anode I6 is connected through aprimary Winding 23 of the transformer19 to the source of unidirectional current supply indicated on thedrawing by 13+. The open-ended transmissionline section 20 is connectedbetween the' control-electrode l8 and I the grounded'cathode'iTin'seriescircuitrelation with a resistor24 and-'a-secondaryWinding 25 of thepulse transformer I91 "The resistor 24 preferably has =aresistancesubstantially equal to the surge impedance-of the transmission linesection 20. "The control electrode I8 is also connect d'tothe cathode |1through 'ajsuitabl'e' grid bias resistor 26 'anda source 'of negativebias potential, such as a battery 21; The pulse output from thedischarge device I is supplied from a tertiary winding 28 on the pulsetransformer |9.

In operation, the pulse generating circuit including the dischargedevice |5 functions in the following manner. When a triggering impulserenders the discharge device conductive, current from the positivepotential source B+ through the primary winding -23 of the pulsetransformer I9 to the .anode'of the'discharge device induces at theungrounded end of the secondary winding 25 of the pulse transformer is apositive potential, thereby driving the control electrode I3 of thedischarge device l5 positive and impressing across the input end of thetransmission line 29 a short voltage pulse. The discharge device I5thereupon begins to conduct. The additional current through thetransformer winding 23 resulting from conduction of the device 65induces an additional positive potential in the winding 25, so that thecontrol electrode is is driven more positive and the discharge device l5driven rapidly to saturation. Conduction continues until the voltagepulse impressedacross the input end of the transmission line 29 travelsto the remote open end and reflects back to the input end. Thisreflected pulse is of such polarity and intensity that it drives thecontrol electrode it ofthe discharge device abruptly negative and beyondcut-ofi', thereby suddenly terminating conduction in the device l5.Thus, the period of the pulses derived from the output of the dischargedevice |5 is determined by the reflection characteristics of thetransmission line section 29, and the frequency of the pulses isdetermined by the frequency of the triggering impulses re-- ceived fromthe discharge device It will, of course, be understood that the maximumpermissible triggering frequency is limited by the time necessary forthe transmission line 20 to discharge through the resistor-26.

A regenerative pulse generating circuit of the type describedimmediately above is described and claimed in the copending applicationof Harold W. Lord, Serial No. 464,033, filed-October 3-1, 1942, issuedJuly 6, 1948, as Patent No. 2,444,782 and assigned to the same assigneeas the instant application.

The voltage pulses derived from the output winding 28 of the pulsetransformer l9 are supplied to the input circuit of anamplifyingelectron discharge device 39 having an anode 3|, a groundedcathode 32, and a control electrode-33. The pulse transformer winding 28is connected between the cathode 32 and control electrode 33 in seriescircuit relation with ,a suitable source of negative bias potential,such as a battery 34 and a grid bias resistor 35 shunted by .a capacitor33. The anode 3| of the amplifying discharge device 39 is connected tothe positive potential source B+ through a primary winding 31 of athree-winding pulse transformer 38. Positive pulses appearing at theupper terminal of the pulse transformer winding 28 in response torecurrent pulsed conduction of the discharge device l5 recurrentlyrender positive the control electrode 33 of the discharge device 33thereby to produce amplified negative voltage pulses upon the anode 3|of the device 39. These amplified pulses appear across the primarywinding 31 of the pulse transformer 38 and induce pulses of oppositepolarity in a pair of oppositely wound secondary windings 39 and 40 ontransformer 38.

The pulse transformer winding39is groundedat one endand connected at itsother end to supply positive pulses through a coupling capacitor 4| ofdeflecting plates 41 to a control electrode or grid 42 of the cathoderay discharge device I. The discharge device I comprises an evacuateddischarge envelope 43 having at one end a grounded cathode 44 and at theother end an anode 45. A suitable source of unidirectional currentsupply, such as a battery 46, is connected between the cathode 44 andanode 45, and the cathode ray discharge is controlled by the grid orcontrol electrode 42. The grid 42 is prol mutually perpendicular axes.

to render the discharge device The pulse transformer winding 45 on thepulse transformer 33 is connected at one end to the positive potentialsource 3+ and at the other end through a unilateral conducting device,such as a diode rectifier 59, to the anode 5|a of an electron dischargedevice SI, and is so disposed that voltage pulses induced in the winding43 in response to voltage pulses in the winding 31 oppose the voltage ofthe source B+. The intensity of the voltage pulses in the winding 49 issubstantially equal to or greater than the intensity of the voltage ofthe source B+. The electron discharge device 5| is preferably of thepentode type and includes, in addition to the anode 5|a, a cathode .52,a control electrode or grid 53, a screen grid 54, and a suppressor grid55. The cathode 52 is grounded and the control electrode 53 andsuppressor grid 55 are connected together and to the cathode. The screengrid 54 is connected through a bias resistor 56 to the source ofunidirectional potential 3+ and through a condenser 51 to ground. Thepositive bias impressed upon the screengrid 54 through the resistor 55is sufficient 52 normally conductive. Furthermore, it is well known thatthe arrangement of the remaining grids in a pentode discharge device ofthis character is such that the magnitude of anode current remainssubstantially constant over a wide range of anode potentials.

A plurality of capacitors 58, 59, and B0 are arranged to be selectivelyconnected between the anode 5|a and cathode 52 (f the discharge device5| by means of a selector switch 6|. As shown on the drawing, the lowcapacitance point 62 of the selector switch 6| is an open circuit. Inthis connection, the only capacitance between the anode-and cathode isthat introduced in the circuit by the interelectrode capacity itself andthe capacitance of the various leads and selector switch parts.

The circuit including the discharge device 5|, the diode rectifier 53,and the capacitors 58, 59, and 50 generates a saw-tooth voltage waveutilized to effect a recurrent timing sweep of the oathode ray beamalong one axis of the fluorescent screen 49. For this purpose, the anode5|a of the discharge device 5| is connected to one of the horizontaldeflection plates 48 in the cathode ray tube 43. The other plate '48 isgrounded, so thal the voltage between the plates 48 is that betweer theanode 5|a and cathode 52 of the dischargl device 5|, as determined bythe selected con denser 58, 59, or 60.

The sweepcircuit described above operates ii the followingmanner toproduce saw-tooth os cillations. When no pulse voltage is presentin theprimary winding 31 of the pulse transformer 38, no voltage is inducedinthe tertiary winding 4!]. Thus, normally the diode rectifier 50 isconductive and current flows from B.-{-. through the tertiary winding59, the diode rectifier 50, and the positively biased pentode dischargedevice 5| to ground. During conduction of the discharge device SE fromthe source 13+, the selected condenser 58, 59 or 5 remains charged to aconstant voltage equal to the voltage drop between the anode 51a andcathode 52 of the discharge device 5|.

Whenever a voltage pulse appears in the transformer Winding 3i, a pulseof voltage is induced in the transformer Winding All in such a directionas to oppose the voltage of the unidirectional voltage source 13+. Sincethe pulse voltage is equal to or greater than the unidirectionalvoltage, the net voltage around the circuit including the dioderectifier 55] and pentode discharge device 5! is reduced to zero orreversed, so that the diode rectifier 5% becomes non-conductive andremain non-conductive for the period of the pulse. During this pulseperiod, the selected charged capacitor 58, 59, or 86 serves as aparallel voltage source and continues the discharge through thedischarge device 5|. Discharge of the capacitor through the source B+ isprevented by the diode 59. As the energy stored in the sweep capacitor58, 59, or 69 diminishes, the voltage of the capacitor decreases.However, a previously pointed out, the current through the dischargedevice 5! remains constant over a Wide range of anode voltages, so thatthe sweep capacitor is discharged at substantially constant current. Asis well known to those skilled in the art, a constant current dischargeof a capacitor effects a substantially .inear decrease in capacitorvoltage. It i the l nearly decreasing sweep capacitor voltage which sapplied between the horizontal deflection plates 3 of the cathode raydischarge device 43.

As soon as the voltage pulse in the pulse transormer winding 46 isterminated, the diode recifier 54'! again becomes conductive and thesource 3+ suppliescurrent to the discharge device 5|. Vhen the rectifierso becomes conductive at the ermination of a pulse, the voltage of theanode Id of the discharge device 5! i raised suddenly, liereby abruptlyto increase the charge and the oltage of the sweep capacitor 58, 59, or66. Thus, 1e cathode ray beam is moved along the horiantal axis of thefluorescent screen 45) at a sub- ;antially constant rate determined bythe rate 3 voltage diminution of the sweep capacitor durlg discharge toestablisha time base for wave aalysis and is suddenly returned to itsstartlg point, when the sweep capacitor voltage is iruptly increasedupon termination of the pulse iltage in the winding 40.

The sweep circuit comprising devices 56 and 51 id capacitors 5t, 58, 653is particularly claimed our copending application Serial No. 663,319,

ed April 19, 1946, which is a division of the prest application.

The positive pulses appearing on the pulse insformer secondary Winding39 are supplied t only through the coupling condenser M to the ritrolgrid 32, but also through a lead 63 to a 1e delay or phase shiftingcircuit 64 to con- |l a trigger pulse generator 65. Pulses in thelnsformer Winding 39 are coincident in time ;h those in the transformerwinding 40 which itrol the discharge of the sweep capacitors 58,

diode rectifier 59, and 60.- Pulses from windings 39 and 40 areamplified in a discharge device 6t and supplied through a transformer 61to trigger orrender operative the source 2 of oscillations to :beobserved oranalyzedr The oscillations to .be analyzed from the source 2are supplied to. thevertical deflection plate 41 of the cathode raydischarge device 43. Thus, the single pulse transformer 38 serves toinitiate the sweep, to simultaneously establish a cathode ray beamthrough controlof the grid or intensifier 42, and torender operative thesource :2 of observed oscil- 'lation through the time delay circuit 64and trigger pulse'gen'erator165; Thus, the trigger pulsesare'synchronized with and delayed in time with respect to the initiationof thebeam sweep.

The time delay'circuit 64 comprises a source of substantially constantunidirectional potential,

such as a battery 68, connected in opposing series.

circuit relation with the pulse transformer secondary winding 39 acrossan integrating circuit consisting of a variable resistor 69 andcapacitor it. A primary winding H of a pulse transformer 72 is connectedacross the condenser ll! through aunilateral conducting device such as adiode rectifier 13. This circuit functions toestablish in thetransformer winding H a recurrent series of voltage pulses delayed intime or phase relation with respect to the series of recurrent voltagepulses appearing in the transformer winding 39.

The operation of the time delay circuit 64 .depends upon thecharacteristics of the integrating circuit 69, it. When no voltage pulseis present in the transformer winding 39 the batteryv 68 maintains thecondenser 'HJ charged-to the battery voltage. Whenever a pulse appearsupon the transformer winding s the pulse voltage opposes the voltage ofthe battery 68. Since the pulse is of substantially rectangular wave;shape and its intensity is greater than the voltage of the battery 68,the sudden reversal of voltage applied to the condenser 70 causes thecon- 1 denser charge to decay exponentially to zero and then to reverse.As soon as the voltage of the condenser 1d reverses, theavoltage'applied to the unilaterally conducting circuit through thepulse transformer winding 'H is reversed, so that the 13 becomesconductive to apply a triggering pulse to the transformer winding H. Itwill thus be evident that the time delay be tween the initiation of apulse in the transformer winding 39 and the initiation of a pulse in thetransformer winding 1! is determined by the time taken for the charge ofthe condenser 70 to decay exponentially to zero and toreversesufficiently to render the discharge device 13 conductive; Thistime is determined by the resistance of the resistor 69 and thecapacitance of the capacitor Hi, and may suitably be controlled byutilizing a variable resistor 59, as indicated on the drawing. Upontermination of each pulse in the transformer winding 39, the battery 68again reverses the charge upon the condenser H1 and brings it back toitsnormal value. The triggering pulse. in the transformer winding "II isnot necessarily of the same duration as the initiating pulse in thetransformer winding 39, but its duration i determined by the length oftime for which the voltage of the capacitor 10 remains reversed by thevoltage, pulse in the transformer winding 39.

The time delay circuit 64 is particularly claimed in our copendingapplication Serial No. 663,320,

the pulse generator 65 delayed in time with respect to pulses in thetransformer winding fiiednprlma sss; hich -iaardivision ofitherprestentiapplication.

The: pulse generating: circuit 65 is similar-to.

that: previously describedcomprising the arline; zflbandz. the:-electron:

tifioial. transmission. discharge. device; [51. The pulse generatingcirouit 65* comprises an; electron discharge device- 14", 3,111artificial transmission. line. 15, a; source: of"

negative: bias; potential. such. as: a. battery 15,. a grid; bias-tresistor 1.119.. resistor; 18: between the transmission. line: 15:.andithercontroL electrode; of

the; electron: dischargedeyice; 14,.and .thepulse;

transformer 1 2; The operation. of the". pulse gen:-

eratingrciircuit: 65: is entirely similar" to. that". of

. the'zpulse; generating circuitpreyiously. described,

the only: difference: being that in: the circuit 65 the: triggering.-pulses. are; supplied through the the: anode ofthe discharge winding: 19of; the pulse. to; the input: circuit oi the amplifying device 'm.Anoutput discharge H rather thandirectly: to;

transformer. '52: supplies andiwezthereforewvishtmhaveitcundierstoodthat: we: intend. in: theappended claims to coverall suchz=modifications as 1 fall? withinthe true spirit andrscopeof:ourrinvention:

whatrwelclaim asmew and desireto secure-by Eetters'Patenizof the- UnitedStates, is: p

1. An apparatus for. analyzing the'charaoteristicsz-of.transientelectricwave derived from a triggeredwave. source comprisin incombina- .j tion, means: for. projecting an electron beam against: asensitivesurface, means for deflecting saidzbeam along:a: .first: axis iresponseto said waves to be analyzed, a source of recurrent-potential.pulses: each. of:v predetermined duration,

; beamdefl'ectingrmeans controlled by saidpulses iorrsweepihg'saidfbeamacross saidJsurfaCe along a second; transverse; axis during. each of'said pulses; each sweeprbeing initiated: at the. leadingedge-ofzaipulse, meanszfor integrating .saidipulses} y to; produce: avoltagawhich; increase rin' one: di-

" rection; throughout said= interval, .means IESPOI'l-v dBYiCEfiE 6 aseries of. recurrentavoltage' pulses have ingalength or perioddetermined by: thechar lation source or generator 2111s connected; tothe verticalr.deflectionplates' 41 of. the cathode ray discharge device:4-3;

By! way: of. illustration of one application-of ouninvention'wehaveillustrated upon the fluorescent: screen 49= atypical picture which.=may appear'in'the'eventithat the oscillation source 2is a radiodirection andrange finding apparatus of the typev comprisinga pulsetransmitter and a receiver'ofecho or reflected. pulses. In accordancewithourinvention, the-cathode ray beam is turned on and. horizontal;sweep. of the beam initiat'edat. theibeginnin'g. of each-pulseappearingz'upon. the transformer winding-:31. The horizontal sweepof:the beam traces a line B2 upon the fluorescent screen 49..synchronously with the initiation: of. the beam. sweep and: in fixedtimedelay relationlwithrespect' thereto, trigger! ing. pulses are suppliedto the source 2 through the; circuit; 84: to render the transmitteropera-- tive'. Upon triggering of the transmitter, aitransmitted';pulse: 83 appears upon the fluorescent screen: 49;byf-op'erati-on of thesource 2 and the vertical? deflectionplatez 4.1;, In"- the' eventthatthe:pulse' 83- encounters a detected object and-is" reflectedbaclctothe receiver of'the source 2, a

neflectedzpulse 8 4"will. appearupon the'fl'uorescent' screenMia-predetermined time. after theipul'se 83, asdetermined'by thedistance between-the source Tandithereflecting object; In this manner,therange of a reflecting obj ect' mayibe determined.

While; we have shown: and described only a .pre-

ferred embodiment". of i ourvinvention, many modificationsnwill' occurto: those skilledin; the art potential, suchasabat- 6.1: are supplied tothe oscillathat source 2. operative The: amplifier 6.6 is. similar to 7pulse each sive. to increase. in said-voltageabove a predeterminedvalueto initiate a delayed trigger pulse, means for triggering said. wave.source in response to said delayed pulsaandmeans for adjusting therate'of increase of said voltage thereby'tdadjust the delay; betweeninitiation of said sweep and-triggering of said'source.

2. An apparatus for. analyzing-the characteristicsof; transientelectric. waves derived from a triggered wave sourcecomprisingincombination,

device having a pair.- of coordinate a a cathode ray. deflecting means;means for impressing said waves to beanalyzed uponone of saiddeflectingmeans,

- meanscomprising a sawtooth generator for'impressing sweep-voltageonrthe other-of said deflecting means, aasourse ofpotential pulses ofsubstantiallyrectangular wave shape and predetermined-pulse width, meansfor synchronizing, said; sweepgenerator-toinitiate each sweep.

uponoccurrence of. the, leading edge of a pulse, means for-integrating;said pulse to produce a voltage which increases in onepolaritythroughout eachpulse;.means for developing. a trigger time, said voltageincreases-to a predetermined value, means for triggering said wavesource-in-synchronism withsaid trigger pulses, and means for varying therate at which said voltage increases; thereby to varythe timedelaybetween initiationof each potential pulse and theicorresponding triggerpulse;

FRANK J. BIAS. HAROLD W. LORD.

REFERENCES CITED- The following references are of recordin thl file oft'hispatent UNITED. STATES PATENTS Number Name Date 2,114,611Schlesinger Apr. 19, 193 22481581: Nforgaard July 8, 194 2,292,835 HeppAug. 11, 194 2,294,863 Hadfield' Sept. 1, 194 2,300,632 Poch Nov; 3, 1942,313,906. Wendt' Mar. 16, 194 23373145: Sensiperet al Apr. 10, 194

